Gasoline dispensing facilities (i.e. gasoline stations) often suffer from a loss of fuel to the atmosphere due to inadequate vapor collection during fuel dispensing activities, excess liquid fuel evaporation in the containment tank system, and inadequate reclamation of the vapors during tanker truck deliveries. Lost vapor is an air pollution problem which is monitored and regulated by both the federal government and state governments. Attempts to minimize losses to the atmosphere have been effected by various vapor recovery methods. Such methods include: “Stage-I vapor recovery” where vapors are returned from the underground fuel storage tank to the delivery truck; “Stage-II vapor recovery” where vapors are returned from the refueled vehicle tank to the underground storage tank; vapor processing where the fuel/air vapor mix from the underground storage tank is received and the vapor is liquefied and returned as liquid fuel to the underground storage tank; burning excess vapor off and venting the less polluting combustion products to the atmosphere; and other fuel/air mix separation methods.
A “balance” Stage-II Vapor Recovery System (VRS) may make use of a dispensing nozzle bellows seal to the vehicle tank filler pipe opening. This seal provides an enclosed space between the vehicle tank and the VRS. During fuel dispensing, the liquid fuel entering the vehicle tank creates a positive pressure which pushes out the ullage space vapors through the bellows sealed area into the nozzle vapor return port, through the dispensing nozzle and hose paths, and on into the VRS.
It has been found that even with these measures, substantial amounts of hydrocarbon vapors are lost to the atmosphere, often due to poor equipment reliability and inadequate maintenance. This is especially true with Stage-II systems. One way to reduce this problem is to provide a vapor recovery system monitoring data acquisition and analysis system to provide notification when the system is not working as required. Such monitoring systems may be especially applicable to Stage-II systems.
When working properly, Stage-II vapor recovery results in equal exchanges of air or vapor (A) and liquid (L) between the main fuel storage tank and the consumer's gas tank. Ideally, Stage-II vapor recovery produces an A/L ratio very close to 1.0. In other words, returned vapor replaces an equal amount of liquid in the main fuel storage tank during refueling transactions. When the A/L ratio is close to 1.0, refueling vapors are collected, the ingress of fresh air into the storage tank is minimized, and the accumulation of an excess of positive or negative pressure in the main fuel storage tank is prevented. This minimizes losses at the dispensing nozzle and evaporation and leakage of excess vapors from the storage tank. Measurement of the A/L ratio thus provides an indication of proper Stage-II vapor collection operation. A low A/L ratio means that vapor is not moving properly through the dispensing nozzle, hose, or other part of the system back to the storage tank, possibly due to an obstruction or defective component.
Recently, the California Air Resources Board (CARB) has been producing new requirements for Enhanced Vapor Recovery (EVR) equipment. These include stringent vapor recovery system monitoring and In-Station Diagnostics (ISD) requirements to continuously determine whether or not the systems are working properly. CARB has proposed that when the A/L ratio drops below a prescribed limit for a single or some sequence of fueling transactions, an alarm be issued and the underground storage tank pump be disabled to allow repair to prevent further significant vapor losses. Many systems employ air flow sensors (AFS), also known as “vapor flow meters” to monitor the amount of recovered vapor to determine if the vapor recovery system is working correctly.
Even with use of AFS, CARB only requires monitoring and alarm generation if the A/L ratio is outside the prescribed limits. Automatic correction of the vapor recovery system is not required. However, if AFSs are used, the vapor recovery system can determine the difference between the desired A/L ratio versus actual performance. In this manner, in addition to monitoring, the vapor recovery system can automatically adjust itself in a closed loop, feedback manner to correct itself. A service call to adjust the vapor recovery system manually can be avoided thereby resulting in lower costs and convenience. A shut down of fuel dispensers may also be avoided. However, this vapor recovery system performance may be detrimentally effected by the introduction of vehicles with Onboard Refueling Vapor Recovery (ORVR) devices that recover refueling vapors onboard the vehicle. CARB also requires that Stage II vapor recovery systems be compatible for both ORVR and non-ORVR fueling transactions.
Vapors produced as a result of dispensing fuel into an ORVR equipped vehicle are collected onboard, and accordingly, are not available to flow through a vapor return passage to an AFS for measurement. Some vapor recovery systems are designed to block the vapor return path when an ORVR-equipped vehicle is being refueled. One such device is disclosed in U.S. Pat. No. 6,810,922, incorporated herein by reference in its entirety. This prevents the ingestion of air into the fuel storage tank, which in turn causes decreased pressure levels within the tank and a lesser possibility for fugitive emissions through the tank vent. With such systems, refueling an ORVR-equipped vehicle results in a positive liquid fuel flow reading, but no return vapor flow reading (i.e. an A/L ratio calculated using the AFS will be equal to 0 or close thereto). Because ORVR fueling transactions cause the AFS measurement to suggest a blockage requiring an A/L adjustment, an ORVR-compatible closed loop, self-adjusting vapor recovery system that employs the AFS will not operate properly.
Thus, there exists a need to provide a self-adjusting ORVR-compatible vapor recovery system that does not improperly adjust the vapor recovery rate during or due to ORVR fueling transactions. The present invention provides a solution to this problem.